1. Field of the Invention
The present invention relates to a semiconductor having a band gap of a mixed crystal formed of a III-V compound semiconductor other than nitride and III-nitrogen compound semiconductor by varying a laminated structure of a super lattice of an atomic layer of the III-V compound semiconductor other than nitride and III-nitrogen compound semiconductor, and relates to a semiconductor device using the same.
2. Description of the Related Art
A blue luminescent device has been studied by using a semiconductor made from a group II-VI, SiC and gallium nitride (GaN) system. Recently, it has been reported that a GaN compound semiconductor exhibits an excellent luminescence at room temperature, and a blue LED using the same has also been developed. Gallium nitride is a material having a band gap of 3.4 eV at room temperature and capable of emitting an ultraviolet light. In view of the characteristics of GaN, an attempt at using a mixed crystal of GaN and III-V group compound semiconductor which has a small band gap with GaN has been made by changing the molar fraction of the mixed crystal to obtain a blue luminescence. In addition, Appl. Phys. Lett. (vol. 63, (1993) 3470) discloses a method for changing an energy level generated in a quantum well layer by using a superlattice structure in the case where a system having the same crystalline structure such as GaAs--AlAs and GaN--AlN is employed, thereby changing a wavelength of luminescence of the quantum well layer.
InN, having the same crystalline structure as GaN, is often used as a material to form a mixed crystal with GaN for obtaining a blue luminescence. Recently, a mixed crystal formed of GaN and a III-V group compound semiconductor other than nitride has been intensively studied. In such a study, attention has been focused on a mixed crystal of GaP.sub.1-x N.sub.x or GaAs.sub.1-x N.sub.x which is formed of GaN and GaP or GaAs (GaP and GaAs have a band gap of 2.78 eV and 1.42 eV (.GAMMA. point), respectively) because a blue luminescent material can be obtained by changing a molar fraction of the mixed crystal.
For example, FIG. 14 shows a schematic view of GaP.sub.1-x N.sub.x mixed crystal. As shown in the figure, GaP.sub.1-x N.sub.x mixed crystal is formed by alternatively laminating a Ga surface 1 and a P.sub.1-x N.sub.x surface 6.
Although GaP.sub.1-x N.sub.x and GaAs.sub.1-x N.sub.x have the above described characteristics, they have a great miscibility gap because a crystalline structure of GaN is different from GaP and GaAs (i.e., GaN has a wurtzite structure and GaP and GaAs have a zincblende structure) and the lattice mismatch is as great as 20%. Accordingly, in the case of GaP.sub.1-x N.sub.x, the obtained mixed crystal is limited to those having a molar fraction of x.ltoreq.0.076 and x.gtoreq.0.91 and in case of GaAs.sub.1-x N.sub.x, to those having a molar fraction of x.ltoreq.0.016 (see Jpn. J. Appl. Phys. Vol. 31 (1992) 3791, Appl. Phys. Lett. Vol. 63 (1993) 3506, Appl. Phys. Lett. Vol. 62 (1993) 1396). As a result, a compound semiconductor and a luminescent device having a desired band gap has not been realized in the form of a mixed crystal.